Elastomeric helicopter rotor head with dynamic and static blade coning and droop stops

ABSTRACT

An elastomeric helicopter rotor having a blade mounted for universal motion about the intersection of the blade pitch change, flapping and lead-lag axes and including blade coning and droop stops, including a ring member rotatably mounted about the pitch change axis on the blade and coning and droop stops constituting segments of circular members whose centers lie on the blade lead-lag axes and with the ring member and coning stop and droop stop members presenting mating surfaces to one another so that as the blade moves in lead-lag motion while the blade ring member is in line or surface mating contact with either the coning stop surface or the static or dynamic droop stop surfaces, a relative rotation will be established therebetween for full support of the blade throughout the lead-lag motion, without affecting blade pitch angle or flapping angle, without preventing independent blade pitch change, and without scuffing of parts.

United States Patent [191 Ferris l ll 3,778,189

Dec. 11, 1973 [75] Inventor: .Donald L. Ferris, Newtown, Conn.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

[22] Filed: Sept. 5, 1972 [21] Appl. No.: 286,509

Primary Examiner-Everette A. Powell, Jr. Attorney-Vernon F. Hauschild [57] ABSTRACT An elastomeric helicopter rotor having a blade mounted foruniversal motion about the intersection of the blade pitch change,flapping and lead-lag axes and including blade coning and droop stops,including a ring member rotatably mounted about the pitch change axis onthe blade and coning and droop stops constituting segments of circularmembers whose centers lie on the blade lead-lag axes and with the ringmember and coning stop and droop stop members presenting mating surfacesto one another so that as the blade moves in lead-lag motion while theblade ring member is in line or surface mating contact with either theconing stop surface or the static or dynamic droop stop surfaces, arelative rotation will be established therebetween for full support ofthe blade throughout the lead-lag motion, without affecting blade pitchangle or flapping angle, without preventing independent blade pitchchange, and without scuffing of parts.

22 Claims, 8 Drawing Figures PATENIEB DEC] 1 I975 SNtEI 1 0f 3 PAIENIEDBEE l 1 I975 SHEUSUFJ FIG. 66

if 3 g M IELASTOMERIC HELICOPTER ROTOR HEAD WITH DYNAMIC AND STATICBLADE CONING AN D DROOP STOPS CROSS-REFERENCE TO RELATED APPLICATIONSubject mattershown and described in this application is shown,descnibedand claimed in a copending application Ser. No. 286,508entitled Elastomeric Helicopter Rotor Head with Dynamic and Static BladeConing and Droop Stops by Robert Rybicki filed on even date herewith.

BACKGROUND OF THE INVENTION .1. Field of the Invention This inventionrelates to droop and coning limit stops for use in helicopter rotors andmore particularly for use in such rotors in which the blade is mountedfrom the hub by mechanism, such as a spherical elastomeric bearing, foruniversal motion about the intersection of the blade pitch change,lead-lag and flapping axes. In particular, to sucha droop stop andconing limit mechanism that rolling motion over mating abutting surfacesexists as the blademoves in lead-lag motion when the blade is in eitherlimit position.

2. Description of the Prior Art In the droop stop art, provisions havenot been made for coning stop and droop stop means for a blade which isuniversally mounted, since blades have not been conventionally somounted inthe prior art articulated helicopter rotor art. In the past,articulated rotor blades have been mounted for motion about selectedaxes, as opposed to universal mounting about a point.

In the prior art, provisions have not been made for coning and drooplimitations on a universally mounted blade for dynamic stops having agreater angular degree of freedomthan the static angular degree offreedom.

In convention droop stop art, such as US. Pat. Nos. 2,614,640;2,628,686; 2,719,593 and 2,906,348, there are no spherical, conical orrolling surfaces to accommodate the universalmotion of a blade fromahub.

Kisovec U.S.Pat. No. 3,282,350 teaches droop and coning stops forusewith elastomeric helicopter rotors, but these stops are of the flat paddesign which do not provide the advantages of the construction taughtherein. This patentdoes not provide constant coning'or droop anglelimitation throughout the lead-lag range, does not providetrollingcontact between the blade and its limit stops, nor the ability to permitnormal pitch changemotion of theblade. When cone 60 of this patent isengaged, the blade is locked in pitch, lead-lag and flapping motion.

Mosinskis US Pat. No. 3,501,250 teaches an articulated helicopter rotorwith an elastomeric bearing mounting and with a droop stop, but of theflat pad and cylindrical roller variety. The cylindrical roller willskid, as opposed to producing rolling contact,since the roller must beconical to produce true rolling contact and the apex of the conicalroller'must be at the intersection of the lead-lag and flapping axes ofthe blade and such would not be the case in this patent even if therollerwere considered to be conical. In addition, this patent does notinclude movable stops.

The disadvantage of the flat pad stops of the prior art is that flat paddesigns are limited to satisfy one single specific degree oflead or lagat one particulardegree of coning. Beyond this specific degree of leador lag,

contact of the stops results in a lesser degree of the required coningangle and high wear on the mating surface due to point or corner contactbetween the stop members. To satisfy two different degrees of angulardroop, static and dynamic, the roller must be conical with its apexcoincident with the center of the centering device, and the mating stopmust also be conical, with its apex coincident with the center of thecenteringde vice. In addition, the mating stop surfaces must beconcentric with the lead-lag axis in order to maintain an identicalstatic and dynamic droop angle through all phases of lead-lag motion.

SUMMARY OF THE INVENTION A primary object of the present invention is toprovide a droop stop and a coning limit stop for a universally mountedhelicopter blade in an articulated rotor wherein the blade is able tomove in lead-lag motion without variation in droop or coning angle,either staticallyon the ground during starting or stopping opera tion ordynamically during flight operation where the angle of droop or coningis at a greater degree, providing full line or surface contact of themating stops and without parts scuffing, without inducing pitch changemotion, and while permitting independent blade pitch change motion, whenthe blade is at either its maximum limit coning angle or its maximumdroop angle, by the use of coning limit and droop stops which arepositioned to intercept and rotatably mate with a ring member mountedfor rotation about the blade pitch change axis. I

In accordance with the present invention, the mating surfaces of theblade mounted ring member and the coning and droop stop members arepreferably conical with the apexes thereof intersecting the point ofintersection of the blade pitch change, lead-lag and flapping axes, sothat true rolling contact is achieved between these parts throughout thefull lead-lag range of blade motion without part scuffing, but could beof the other shapes or curvatures disclosed herein in lightweight,light-load installations where pure rolling contact would not beabsolutely essential.

Inaccordance with the present invention, when the blade is at either ofits coning or flapping limit stops, lead-lag motion can take placewithout changing the angle of coning flapping.

In accordance with still a further object of the present invention, thispermitted lead-lag motion at the limit stops occurs without scuffingbetween blade and hub mounted parts.

In accordance with a further aspect of the present invention, acentrifugally responsive mechanism is utilized with the dynamic droopstop to constitute a static droop stop when the blade is at lowrotational speed operation or stopped. i

In accordance with the teaching herein, the blade mounted rotatable ringmember, the coning limit stop, the dynamic droop stop and the staticdroop stop preferably have conically selectively shaped surfaceswhoseapexes are positioned at the point of intersection of the blade pitchchange, flapping and lead-lag axes, or mating spherical surfacescentered respectively on the blade pitch change and lead-lag axes. Itmay be considered that the coning limit stop and the dynamic and staticdroop stops are segmented mating spheres resulting in a matching, matingconcave-convex surface.

It is a further object of this invention to utilize concave-convexmating surface contact between blade mounted and hub mounted droop andflap limit members, and corresponding surfaces on the centrifugallyactuated stop member, to wedge the centrifugally actuated stop member inposition to prevent its disengagement due to blade load when thehelicopter is on the ground and the rotor is static.

Other objects and advantages of the present invention may be seen byreferring to the following description and claims, read in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial side view of anarticulated helicopter rotor, partially broken away for illustration,which shows the static and dynamic droop stop and coning limit stop inan environment of an articulated helicopter rotor in which the blade issupported from the rotor hub by a spherical elastomeric bearing so as tobe universally movable about the intersection of the blade pitch change,lead-lag and flapping axes.

FIG. 2 is an enlarged side view of the static and dynamic droop stop andconing limit stop.

FIG. 3 is a view taken along line 3-3 of FIG. 2.

FIG. 4 is a schematic top view representation of the coaction betweenthe droop stop member and the blade mounted rotatable ring member of theFIG. 2 embodiment.

'FIG. 5 is a side view of the construction shown in FIG. 4 and withflapping limit stop added.

FIGS. 6a and 6b are side views of modifications showing concave-convexcontact surfaces between the droop stop member, the flapping limit stopmember and the blade mounted rotatable ring member of the FIG. 2embodiment.

FIG. 7 is a section along line 77 of FIG. 3 for the modification wherethe contacting surfaces are spherical.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 we see'articulated helicopter rotor 10 which comprises a'rotor' hub 12 mountedfor rotation about axis of rotation 14. A plurality of blades, one ofwhich is shown at 16, extends substantially radially from the hub andare mounted therefrom for rotation therewith about axis 14 to generatelift. Basically, the blade 16 is supported from hub 12 through sphericalelastomeric bearing 18 or other suitable mechanism for universal motion.Bearing 18 is mountd between hub supported yoke or loop member 20 andblade connected yoke or loop member 22, which yoke members interlock toposition elastomeric spherical bearing 18 therebetween. Morespecifically, hub arm 24 is a portion of hub link member 20 and servesto support blade centering bearing 26 and the inner race 28 of sphericalbearing 18. The outer race 30 of spherical bearing 18 is connected toblade yoke 22 so that blade 16 is supported from hub 12 throughspherical elastomeric bearing 18 for universal motion about theintersection 37 of pitch change axis 32, lead-lag axis 34 and flappingaxis 36.

Elastomeric bearing 18 preferably includes spaced spherical metalliclaminates encased in elastomer and spherically centered aboutintersection 37, as are surfaces 38 and 40 of the bearing races. Thelaminates are joined to one another with the outer elastomer joined tosurface 40 and the inner elastomer to surface 38. Bonding is thepreferred method of joining.

Blade sleeve 42 connects to blade yoke member 22 through conventionalnut and bolt members 44, which extend through the aligned holes in theoverlapping flanges thereof, such as those shown at 46, 48 and 50. Stubshaft 52, which is concentric about pitch change axis 32, is connectedto sleeve 42 by conventional bolt members 54 and is preferably shaped todefine centering pin 56. Centering pin 56 is also concentric about axis32 and supports the inner race 59 of the spherical centering bearing 27,which is supported by hub arm 24 to be universally mounted about point37. It will be noted that with this construction, blade 16 is mountedfrom hub 12 through spherical bearing 27 for universal motion about theintersection of the pitch change axis 32, the lead-lag axis 34 and theflapping axis 36 at common point 37.

Droop stop ring is mounted for rotation about axis 32 on stub shaft 52and is supported from the shaft by journal 72. Ring 70 is free to rotatewith respect to stub shaft 52 because of the solid or dry lubricant orselective plating between ring surface 74 and journal surface 76.Surface of ring 70 is of selected shape, to be described in greaterparticularity hereinafter, so that it will matingly engage surface 82 ofconing limit stop member 84 when the blade is at its maximum permittedconing angle, and so that it will matingly engage surface 86 of staticdroop stop member 88 or surface 90 of dynamic droop stop 92. It isimportant that, when blade 16 is at its maximum coning and surface 80 isin contact with surface 82, the blade can move in lead-lag motionwithout scuffing of surfaces 80 and 82 and without inducing pitch changeor decrease to the maximum coning angle, and while permittingindependent blade pitch change motion. This is accomplished by havingring 70 rotate about pitch change axis 32 as it travels in rolling linecontact along surface 82. The same is true, when surface 80 is incontact with surfaces 86 or 90 of the droop stops, so that blade 16 ispermitted to move in lead-lag motion about axis 34 due to the rotationof ring 70 about axis 32 as it remains in rolling line contact with androtates with respect to surfaces 86or 90.

A conventional lead-lag damper, not shown but preferably of theconventional hydraulic cylinder-piston type, connects to blade yokemember 22 through damper bearing 94, which connects for universal motionabout centering pin 96. Bearing outer race 98 is connected to thelead-lag damper.

Surfaces 82, 86 and 90 are shaped as segments of circular members whichlie in a substantially horizontal plane and which circular members arecentered on lead-lag axis 34. The cross-sectional shape of each is acircle segment concentric about lead-lag axis 34.

Dynamic droop stop member 92 and static droop stop member 88 will bedescribed in greater particularity hereinafter.

By viewing FIG. 2, it will be noted that as blade 16 flaps or conesupwardly about flapping axis 36, surface 80 of rotatably mounted ring 70will eventually bear against surface 82 of hub mounted coning anglelimit member 84 to prevent a further increase in blade flapping motion.Surfaces 80 and 82 are selectively contoured to be in mating surfaceengagement as blade 16 moves in lead-lag motion about axis 34, whilering 70 and limit stop 84 continue in line rolling contact, and suchoccurs without scuffing, and without inducing pitch change and flappingangle change due to the rotation of member 70 with respect to member 84.Similarly, as blade 16 flaps downwardly during normal rotor operation,eventually surface 80 of ring 70 contacts surface 90 of dynamic droopstop 92 to prevent further downward flapping of blade 16. Again,surfaces 90and 92 are selectively shaped so that they will be in matingline rolling engagement throughout as blade 16 moves in lead-lag motionabout axis 34, with ring 70 rotating with respect to stop 92to preventpitch change, or flapping motion, or scuffing therebetween. In additionto dynamic droop stop 92, the FIG. 2 construction also includes staticdroop stop 88, which is substantially a U-shaped member pivotallyconnected at the ends of its legs at pivot points, such as 94, tobracket members 96, which are supported in conventional fashion from hub12. Static droop stop 88 is shown in its low rpm or ro tor-stoppedposition in FIG. 2 and it should be borne in mind, that, due tocentrifugal force, as rotor rpm increases, static droop stop 88 willpivot about pivot point 94 in a clockwise direction so as to no longerbe positioned between surfaces 80 and 90 of ring 70 and dynamic. droopstop 92, respectively. As best shown in FIG. 3, static droop stop 88includes surface 86 which matingly engages surface 80 of ring 70 whenstatic droop stop 88 is in its FIG. 2 position. Surface 86 is alsoselectively shaped to matingly engage surface 80 of ring 70 at all timesas blade 16 leads and lags about lead-lag axis34, while ring'70 rotateswith respect to static stop 88. It will also be noted that static stop88 includes surface 100, which corresponds in shape to surface 90 ofdynamic droop stop 92 for clearance purposes anu full surface contact soas to allow static droop member 88 to overlap stop 92.

Surfaces 80, 82,86 and 90 can be of different shapes asshown in FIGS.46,but it should be bornein mind that his important that surfaces82, 86 and90 matingly engage surface 80 of rotatable ring 70 in mating linecontact to lend full support thereto and remain in mating engagement asblade 16 moves in lead-lagmotion while these surfaces are in contact,with ring 70 rotatingwith respect tosurfaces 82, 86 M90 to preventmetallic scuffing, blade pitch or lag angle change, and to allowindependent blade pitch change motion within tively, are shown asfrustoconical in shape and as being portions of coneswhose apexesintersect at the point of intersection 37 of axes 32, 34 and 36. This isbest shown in FIG. 5. As best shown in FIG. 4, while frustoconicalsurfaces 80 and 90 of ring 70 and dynamic droop stop 92 are incontinuous line rolling contact, ring 80 may rotate with respect tostop92 as blade 16 moves in lead-lagimotion about axis 34. This relativerotation occurs "without changing the blade droop or flapping orpitchangle. FlG.-4 showering 70 in two positions, in the solid linenonlagposition and in the phantom lead or lag position. It will benotedby viewing FIGS. 4 and 5 that dynamic droop stop surface 90 is atleast a segment ofa conical member lying horizontally or in a planeparallel to pitch change axis 32 and concentric about lead-lag axis 34.

As best shown in FIG. 5, flapping stop limit member 84 is also at leasta segment of a cone lying in a horizontal plane or in a plane parallelto pitch change axis 32 and concentric about lead-lag axis 34 andpresents frustoconical surface 82 for contact with surface 80 of ring70, which frustoconical surface 82 is formed from a cone whose apex isat the aforementioned point of intersection 37 between axes 32, 34 and36. The advantage to be gained by the FIG. 4 and 5 construction in whichsurfaces 82 and 90, and surface 86 ofFIG. 3, are frustoconical withapexes positioned at point of intersection 37 and concentric about axis34 and surface 80 of ring member is also frustoconical with apex positioned at point of intersection 37 and concentric about leadla'g axis32, when centered, is that pure, rolling, line contact occurscontinuously between surfaces and or 80 and 82, respectively, when bladeis in its droop limit or flap limit position and moving inlead-lag'motion without inducing blade pitch change and without scuffingof mating parts. This is my preferredembodiment.

As best shown in FIG. 4a, surface 80 of rotatable ring 70 can be ofspherical shape centered about a point 101 on pitch change axis 32 ofradius R and, dynamic droop stop surface 90 is of equal or correspondingradius R about point 101 when the surfaces contact, and are shaped to bea ring segment concentric about axis 34. Surface 82 of coning limit stop84 is a concave surface corresponding in shape to spherical surface 80and is accordingly of radius R when point lfll moves with I pitch changeaxis 32 about pointof intersection 37 or faces 80 and 86 were incontact. Surface 86 would'also be concentric about lead-lag axis 34. l

FIG. 6b illustrates that the curvature of surfaces 90, 80 and 82 can beat radius R centered abovelead-lag axis 34. V i

The advantage to be gained by the constructions is that, as best shownin FIG. 7, the static droop stop member 88 is shaped to be locked inwedged position between members 70 and 92'when the blade is at rest sothat the weight of the blade does not cause static droop stop member 88to be forced out of position from between members 70 and 92.

It will accordingly be seen that. with or without the flapping limitmember 84 of FIG. 1, blade 16 may droop downwardly until surface 80 ofrotatable ring 70 contacts either mating surface 86 or 90 of staticordynamic droop stops 88 and 92, respectively, and blade 16 can movefreely in lead-lag motion without affecting blade pitch, whilepermitting blade pitch change, and while permitting the maximum droopangle to remain constant, and without scuffing between the surfaces incontact, all due to the continuous line contact and rolling motion whichexists between surface 80 of ring 70 and the corresponding matingsurface 82 of flap limit stop 84 or surfaces 86 or 90 of droop stops 88or 92. Blade 16 can move freely in lead-lag motion about axis 34 withoutaffecting blade pitch,-while permitting blade pitch change independentlyof blade lead-lag motion,

and while permitting the upward flapping or lower drooping blade angleto remain constant, and without scuffing between the surfaces incontact, all due to the continuous contact and rolling motion whichexists between surfaces 80 of ring 70 and the corresponding matingsurface 82 of flap limit stop 84 or surfaces 86 or 90 of droop stops 88or 92.

l wish it to be understood that 1 do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

I claim:

1. An articulated helicopter rotor including:

A. a rotor hub adapted to be mounted for rotation,

B. at least one helicopter blade projecting substantially radially fromsaid hub and having a pitch change axis, a lead-lag axis, and a flappingaxis intersecting at a common point,

C. means supporting said blade from said hub for universal motion aboutthe intersection of said axes,

D. a ring member mounted on said blade for rotation relative theretoabout said pitch change axis and at a station radially outward of saidpoint of intersection and having:

I. a selectively shaped surface positioned to move toward said hub assaid droops downwardly,

E. a droop stop member connected to said hub and having a selectivelyshaped surface positioned to intercepting said ring member when saidblade droops downwardly to a first selected angle and which surface isshaped to present a corresponding mating surface with said ring membersurface to effect relative rotation therebetween as said blade moves inlead-lag motion when said surfaces are in contact.

2. A rotor according to claim 1 wherein said droop stop member surfaceis conical with the apex thereof located at said point intersection ofsaid axes.

3. A rotor according to claim 1 wherein the mating surfaces of saiddroop stop member and said ring member are concave-convex for matingengagement.

4. A rotor according to claim 1 wherein selectively shaped surfaces ofsaid ring member and droop stop member are frustoconical with the apexesthereof positioned at said point of intersection.

5. A rotor according to claim 1 and including a centrifugally responsivemember having a first selectively shaped surface corresponding to saidselectively shaped surface of said ring member and a second selectivelyshaped surface corresponding to said selectively shaped surface of saiddroop stop member and being pivotally mounted with respect to said bladeand hub for motion between a first position wherein said pivotallymounted member is positioned between the selectively shaped surfaces ofsaid ring member and said droop stop member at low rotor speeds or whenthe rotor is stopped and oriented so as to present its first selectivelyshaped surface to said selectively shaped surface of said ring memberfor mating engagement therewith and to present its second selectivelyshaped surface to said selectively shaped surface of said droop stopmember for mating engagement therewith when said blade droops downwardlybeyond a second selected angle, and a second position remote from saidring member and said droop stop member.

6. A rotor according to claim 5 wherein said droop stop member is wedgeshaped between said first and second selectively shaped surfaces so thatsaid droop stop member is locked in position between said ring memberand said droop stop member when in said first position.

7. A rotor according to claim 6 wherein said selectively shaped surfacesof said droop stop member, said ring member and said centrifugallyresponsive member are arcuate with said first selectively shaped surfaceof said centrifugally responsive member shaped to be in matingengagement with and corresponding to said selectively shaped surface ofsaid ring member and with said second selectively shaped surface of saidcentrifugally responsive member shaped to be in mating engagement withand corresponding to said selectively surface of said droop stop memberwhen said centrifugal responsive member is in said first position.

8. A rotor according to claim 5 wherein said selectively shaped surfacesof said ring member and said droop stop member and said selectivelyshaped surfaces of said centrifugally responsive member are shaped sothat concave convex mating occurs between said first selectively shapedsurface of said centrifugally responsive member and said ring member andbetween said second selectively shaped surface of said centrifugallyresponsive member and said droop stop member when said centrifugallyresponsive member is in said first position.

9. A rotor according to claim 8 wherein said centrifugally responsivemember is of wedge-shaped cross section between said first and secondselectively shaped surfaces thereof so that said centrifugally actuatedmember is locked in said first position when its first and secondselectively shaped surfaces, respectively, matingly engage theselectively shaped surfaces of said ring member and said droop stopmember.

10. A rotor according to claim 5 wherein said second selected angle isless than said first selected angle.

11. A rotor according to claim 1 wherein said support means includes aspherical elastomeric bearing centered about said point of intersectionand having alternate elastomeric and rigid laminates.

12. A rotor according to claim 1 wherein said droop stop member is acircular segment which lies in a substantially horizontal plane and thecenter of which lies on the lead-lag axis.

13. A rotor according to claim 1 and including a coning limit stopmember connected to said hub and having a selectively shaped surfacepositioned to intercept said ring member when said blade flaps or conesupwardly to a selected angle and which surface is shaped to present acorresponding mating surface with said ring member surface to effectrelative rotation therebetween as said blade moves in lead-lag motionwhen said surfaces are in contact.

14. A rotor according to claim 13 wherein said coning limit member is acircular segment which lies in a substantially horizontal plane, thecenter of which lies on said lead-lag axis.

15. A rotor according to claim 1 wherein said selectively shaped surfaceof said ring member and said selectively shaped surface of said droopstop member are frustoconical with apexes positioned at said point ofintersection and concentric about said pitch change axis and saidlead-lag axis, respectively, and which are shaped to form line contactwhen said selectively shaped surfaces abut and rotate relative to oneanother.

16. A rotor according to claim 1 wherein said selectively shaped surfaceof said ring member and said selectively shaped surface of said droopstop member are shaped to be spherical about either a point on the pitchchange axis or a point on the lead-lag axis so as to be in line contactwhen said surfaces engage and rotate relative to one another.

17. A rotor according to claim wherein said selectively shaped surfacesof said ring member, said droop stop member and said centrifugallyresponsive member are frustoconical with apexes located at said point ofintersection of said pitch change, lead-lag and flapping axes andwherein said selectively shaped surfaces of said droop stop member andsaid centrifugally responsive member are concentric about said lead-lagaxis and said selectively shaped surface of said ring member isconcentric about said pitch change axis so that said blade may move inlead-lag motion and at constant droop angle and without altering bladepitch as said ring member and said droop stop member rotate relative toeach other as said selectively shaped surfaces thereof arein continuousengagement.

18. A rotor according to claim and including a coni'ng limit stop memberconnected to said hub and having a selectively shaped surface which isfrustoconical with its apex positioned at said point of intersection andconcentric about lead-lag axis, and which is shaped to form line contactwhen said selectively shaped surfaces of said ring member and saidconing angle limit member rotate relative to one another while incontinuous contact and with said blade at constant flapping angle.

19. A rotor according to claim 16 and including a coning angle limitstop member connected to said hub and having a selectively shapedsurface which is spherical about a point on the lead-lag axis or thepitch change axis and which corresponds in curvature with saidselectively shaped surface of said ring member and is positioned tocontact said selectively shaped surface of said ring member when saidblade coning angle reaches a selected maximum so as to be in linecontact.

when said selectively shaped surface of said ring member and said coningangle limit stop member engage and rotate relative to one another.

20. A rotor according to claim 5 wherein said selectively shapedsurfaces of said ring member, said droop stop member, and saidcentrifugally responsive mem' ber are spherical about points located onsaid pitch change axis or said lead-lag axis and of common radius andwherein said selectively shaped surfaces of said droop stop member andsaid centrifugally responsive member are concentric about said lead-lagaxis, and said selectively shaped surface of said ring member isconcentric about said pitch change axis.

21. An articulated helicopter rotor including:

A. a rotor hub adapted to be mounted for rotation,

B. at least one helicopter blade projecting substantially radially fromsaid hub and having a pitch change axis, a lead-lag axis and a flappingaxis intersecting at a common point,

C. means supporting said blade from said hub for universal motion aboutthe intersection of said axes,

D. a ring member mounted on said blade for rotation relative theretoabout said pitch change axis and at a station radially outward of saidpoint of intersection and having:

1. a selectively shape surface positioned to move toward said hub assaid blade droops downwardly, wherein said selectively shaped surface isfrustoconical concentrically about the pitch change axis and having anapex at said common point,

E. a droop stop member connected to said hub and having a selectivelyshaped surface positioned to intercept said ring member selectivelyshaped surface when said blade droops downwardly to a first selectedangle and which surface is frusto-conical concentrically about saidlead-lag axis and having an apex positioned at said common point so thatwith said frustoconical surfaces in continuous line contact, said blademay move in lead-lag motion at constant droop angle and withoutaffecting blade pitch, while said ring member rolls relative to saiddroop stop member without part scuffing.

22. A rotor according to claim 21 wherein said selectively shapedsurfaces of said ring member and said droop stop member are segmentedspheres concentric about said pitch change axis or said lead-lag axis.

1. An articulated helicopter rotor including: A. a rotor hub adapted tobe mounted for rotation, B. at least one helicopter blade projectingsubstantially radially from said hub and having a pitch change axis, aleadlag axis, and a flapping axis intersecting at a common point, C.means supporting said blade from said hub for universal motion about theintersection of said axes, D. a ring member mounted on said blade forrotation relative thereto about said pitch change axis and at a stationradially outward of said point of intersection and having:
 1. aselectively shaped surface positioned to move toward said hub as saiddroops downwardly, E. a droop stop member connected to said hub andhaving a selectively shaped surface positioned to intercepting said ringmember when said blade droops downwardly to a first selected angle andwhich surface is shaped to present a corresponding mating surface withsaid ring member surface to effect relative rotation therebetween assaid blade moves in lead-lag motion when said surfaces are in contact.2. A rotor according to claim 1 wherein said droop stop member surfaceis conical with the apex thereof located at said point intersection ofsaid axes.
 3. A rotor according to claim 1 wherein the mating surfacesof said droop stop member and said ring member are concave-convex formating engagement.
 4. A rotor according to claim 1 wherein selectivelyshaped surfaces of said ring member and droop stop member arefrustoconical with the apexes thereof positioned at said point ofintersection.
 5. A rotor according to claim 1 and including acentrifugally responsive member having a First selectively shapedsurface corresponding to said selectively shaped surface of said ringmember and a second selectively shaped surface corresponding to saidselectively shaped surface of said droop stop member and being pivotallymounted with respect to said blade and hub for motion between a firstposition wherein said pivotally mounted member is positioned between theselectively shaped surfaces of said ring member and said droop stopmember at low rotor speeds or when the rotor is stopped and oriented soas to present its first selectively shaped surface to said selectivelyshaped surface of said ring member for mating engagement therewith andto present its second selectively shaped surface to said selectivelyshaped surface of said droop stop member for mating engagement therewithwhen said blade droops downwardly beyond a second selected angle, and asecond position remote from said ring member and said droop stop member.6. A rotor according to claim 5 wherein said droop stop member is wedgeshaped between said first and second selectively shaped surfaces so thatsaid droop stop member is locked in position between said ring memberand said droop stop member when in said first position.
 7. A rotoraccording to claim 6 wherein said selectively shaped surfaces of saiddroop stop member, said ring member and said centrifugally responsivemember are arcuate with said first selectively shaped surface of saidcentrifugally responsive member shaped to be in mating engagement withand corresponding to said selectively shaped surface of said ring memberand with said second selectively shaped surface of said centrifugallyresponsive member shaped to be in mating engagement with andcorresponding to said selectively surface of said droop stop member whensaid centrifugal responsive member is in said first position.
 8. A rotoraccording to claim 5 wherein said selectively shaped surfaces of saidring member and said droop stop member and said selectively shapedsurfaces of said centrifugally responsive member are shaped so thatconcave convex mating occurs between said first selectively shapedsurface of said centrifugally responsive member and said ring member andbetween said second selectively shaped surface of said centrifugallyresponsive member and said droop stop member when said centrifugallyresponsive member is in said first position.
 9. A rotor according toclaim 8 wherein said centrifugally responsive member is of wedge-shapedcross section between said first and second selectively shaped surfacesthereof so that said centrifugally actuated member is locked in saidfirst position when its first and second selectively shaped surfaces,respectively, matingly engage the selectively shaped surfaces of saidring member and said droop stop member.
 10. A rotor according to claim 5wherein said second selected angle is less than said first selectedangle.
 11. A rotor according to claim 1 wherein said support meansincludes a spherical elastomeric bearing centered about said point ofintersection and having alternate elastomeric and rigid laminates.
 12. Arotor according to claim 1 wherein said droop stop member is a circularsegment which lies in a substantially horizontal plane and the center ofwhich lies on the lead-lag axis.
 13. A rotor according to claim 1 andincluding a coning limit stop member connected to said hub and having aselectively shaped surface positioned to intercept said ring member whensaid blade flaps or cones upwardly to a selected angle and which surfaceis shaped to present a corresponding mating surface with said ringmember surface to effect relative rotation therebetween as said blademoves in lead-lag motion when said surfaces are in contact.
 14. A rotoraccording to claim 13 wherein said coning limit member is a circularsegment which lies in a substantially horizontal plane, the center ofwhich lies on said lead-lag axis.
 15. A rotor according to claim 1wherein said selectively shaped surface of said ring Member and saidselectively shaped surface of said droop stop member are frustoconicalwith apexes positioned at said point of intersection and concentricabout said pitch change axis and said lead-lag axis, respectively, andwhich are shaped to form line contact when said selectively shapedsurfaces abut and rotate relative to one another.
 16. A rotor accordingto claim 1 wherein said selectively shaped surface of said ring memberand said selectively shaped surface of said droop stop member are shapedto be spherical about either a point on the pitch change axis or a pointon the lead-lag axis so as to be in line contact when said surfacesengage and rotate relative to one another.
 17. A rotor according toclaim 5 wherein said selectively shaped surfaces of said ring member,said droop stop member and said centrifugally responsive member arefrustoconical with apexes located at said point of intersection of saidpitch change, lead-lag and flapping axes and wherein said selectivelyshaped surfaces of said droop stop member and said centrifugallyresponsive member are concentric about said lead-lag axis and saidselectively shaped surface of said ring member is concentric about saidpitch change axis so that said blade may move in lead-lag motion and atconstant droop angle and without altering blade pitch as said ringmember and said droop stop member rotate relative to each other as saidselectively shaped surfaces thereof are in continuous engagement.
 18. Arotor according to claim 15 and including a coning limit stop memberconnected to said hub and having a selectively shaped surface which isfrustoconical with its apex positioned at said point of intersection andconcentric about lead-lag axis, and which is shaped to form line contactwhen said selectively shaped surfaces of said ring member and saidconing angle limit member rotate relative to one another while incontinuous contact and with said blade at constant flapping angle.
 19. Arotor according to claim 16 and including a coning angle limit stopmember connected to said hub and having a selectively shaped surfacewhich is spherical about a point on the lead-lag axis or the pitchchange axis and which corresponds in curvature with said selectivelyshaped surface of said ring member and is positioned to contact saidselectively shaped surface of said ring member when said blade coningangle reaches a selected maximum so as to be in line contact when saidselectively shaped surface of said ring member and said coning anglelimit stop member engage and rotate relative to one another.
 20. A rotoraccording to claim 5 wherein said selectively shaped surfaces of saidring member, said droop stop member, and said centrifugally responsivemember are spherical about points located on said pitch change axis orsaid lead-lag axis and of common radius and wherein said selectivelyshaped surfaces of said droop stop member and said centrifugallyresponsive member are concentric about said lead-lag axis, and saidselectively shaped surface of said ring member is concentric about saidpitch change axis.
 21. An articulated helicopter rotor including: A. arotor hub adapted to be mounted for rotation, B. at least one helicopterblade projecting substantially radially from said hub and having a pitchchange axis, a lead-lag axis and a flapping axis intersecting at acommon point, C. means supporting said blade from said hub for universalmotion about the intersection of said axes, D. a ring member mounted onsaid blade for rotation relative thereto about said pitch change axisand at a station radially outward of said point of intersection andhaving:
 22. A rotor according to claim 21 wherein said selectivelyshaped surfaces of said ring member and said droop stop member aresegmented spheres concentric about said pitch change axis or saidlead-lag axis.